Treatment of rubber



Patented Mar; 26, a

' ass s mssts t Unit states New Xorlg, MN: Y'., a corporation of New [N0 Drawing. ApplicatienAugust l l 1e32,;

Serial -Weir:

3 Claims ns-Izs) a invention relates to. improvements in the treatment oi rubber and particularly to improvements in.theplasticationi'of rubber and rubberlike materials. y

An object of this invention is to provide a method of increasing" the rate of breakdown of crude rubber during masticationbymeans of. the usual masticating machinery, Another object is to provide aprocess wherebya soiterbrokendown ubb r m bsprmi ssdin asivssiime h ma t cation than is possible under the usual conditions l ic ipn- "Another Qhieszt is were? process of breaking downcrude-rubber whereby substantial savings intime, labor, power conum tion n eq me costs ayb rea iz A' iu'rtherobject is to provide, a process whereby thC- Out ut of a givenirnasticatingeq i ment-rnay besubstantially increased. 1A still further Object is'to provide a softened or broken down' crude 1 rubber having desirable physical b fb erties. Other objects will be apparent" from the following description. I 1 Y {It'is' customary to'pl'asticize crude rubber on a roll-mill or inan internal grinder before mixing in the compounding ingredients, j-such as fillers, pigments, and vulcanizing ingredients suchas accelerators, sulphur, .etc.. The operation. nor;

mally requires from 30-40, min. to; several hours, depending on. the softness desired, and is carried out eithericontinuously, or intermittently :with intervening rest periods. So called softeners? s ch a a t a i oils, nd ta s usua -am dre insii psnsib s actor pmps nd n y wh n added to crude rubberon the mill actually decrease the degree of breakdown which can be before-further processing]: This. effect is due to the'tliixotropic'naturej sigma; mass, n s distinct 1mm thehardening due to cool of the rubber[ l ixotropic' hardening or therubber stock" is bstamnuy avoided" by the present invention.

..,Accordingly the invention treating crude rubber during the preliminary breakdown oi'm sucatmg period. with a reagent to increase the rate of breakdown of the rubber,

said reagent being selected from the group co-n sistin g of lead, diog ide and lead sesqui'oxide aforementioned reagents.

. cation.

tion may be delayed until further processing of broadly comprises prio to the, incorporationfoi the usu pounding an ori'vuloanizing ingre strangelydo not," when addedlto cruderub ,er', produce the effects resultingffrorn t 4 the.

The reagent is incorporated in the 'iubber,"sub-' stantially as soon as it rhasibeen masticated to a coherent mass or sheet, which condition is usually reached after a few minutes of preliminary masti-l Q V .Mastication is continued after adding, the reagent or reagents, or the further .mastica the rubberis desired. Generally, thecompound insand/ vulqanizins nsredienisshqu d 19? 99. added until the rubber has reached the desired degree of softness. Certain matennstgndlm destroy the plasticizing powers of-the reagents and sliculd'not be added to the rubber during. the breakdown; for example, sulphur ,readily ifeacts upon the'lead dioxide to destroy its plasticizing action. f3: a I .Th'e reagents may be used in variousamounts but it is preferred touse them in uantitiesjrpm about 0.2 %.t0. a u 1,70% o theei h f; 11 1 ber used. It is to be understood that larger am unts or t eir asent rm y e use and tr a will determine the proper amount for'the desired result. The prefered temperature: range I withinjrwhich the rubber is treated is the, range commonly ernfe ployed in'the breakingdown Ofcru'dejrubber; that alth isbi higher temperatures may be sed, i de ssm lafiemre aire a'sh hlas 260 F u ee u si fwi hs si st rv resu t The e e (if-the I ocess are less noticeable when'th'e process is carried out with 'thetemperatur e o fthe' rubber muchtemw 140 order to'obtain the benefits of the invention, such asieaucea power demands, to the fullest degree, it is preferable alsov to carry out the pre liminar'y working of. the rubber,prior to the" incorporation of the breakdowns-accelerating reagent,- on 'or' in a-preheated. mill ratherthanto start with a cold. mill? Under the conditions of the present process the reagent is decomposed duringtheplasticizing process, and substantially no undecoinposed reagent is present during the subsequent operations of compounding and vulcanizingpfor ezgamplea p t n ofr bberwhich.hadbssnrlasii efi w the aid of lead dioxide according tojtheipr ent invention} was submittedltio' .a; delicatdt for traces of l ss deride an w j i u tain none, It is evident that'the reagentbec edue 'iifissr Pre m s a i 'i r (P5 94), landsaid treatrnent divalent stage represented by leadiiliiorioxide i or corresponding lead salts; t

shear and ate. temperature. of 212;F."1,V

The plasticities as given in the examples below,

represent the relative viscosities of the respectivegi rubber samples and were-determinedbymeasure ing the relative resistance of the samples tosim- 1: pie shearing stress at a constant avera ate of The invention is illustrated as} follows, '3 the parts-and percentages being by weight:

r 'ma pze 1.- --A quantity of smoked-sheet was ."blended by milling for three'minutes' andivvas then divided into portions'of 600 grams each.

Asa control, one such portion was then milled for 8 min. at}200 F. without the addition of any reagent." To each oftwo other'portions respectively reagentswere addedf'as indicate'd'in Table I land the. treated portions were then each milled for '8'r'nin. at 200 F."I Samples .of eachoi the portionswere takenijust prior to and also at the completion of the" 8 m. millin p riod and the plasticity of each sample was determined.

esuli e im m Taarfr: I-

" Plasticity v 7: PercentjChemical reagent gf a gg "After-8 decreasfi in a i! r r min. viscos y 30 Initial mining at 200 r m; 7115 10.5 1.4 B. Lead dioxide; 0.5 7l;5 60.5 16.0 0. Lead digxide n I 71.5 56.5 21 0 ;,,{1t ig obviou nomlthe. awe datarthat the treated portions Band C .underwent ayery substantial softening during a period of timein which the plasticity of the control portion -A re- 2 mainedpractic'ally:constantl 7 Example 2. A tire tread mix B'was prepared in" which the" rubber used was smoked sheets which had previouslybeen brokendown with the aid of 0.5% of lead dioxide according tothe presen i v n i n. The; u u ,,Vs t r i w 'omittedfrom this Another mix A was prebroken-down rubbers before compounding, and

lsl compositions; 1 L: e c,

pared according w the same basic formula but employing smoked ,4 sheets brokenj down in the ordinary manner. To mix A were, also" added "the necessary amountsof soft'eners, according tocommon practice; pine tar and'palm oilbeing used inthis instance. The amount oiYvulcaniza-r tionraccelerator was adjusted so as tofgi'v e the samerate of cure in bothmixes, Determinations were mad'e of the plasticities "of the respective of the compounded mixes. [Slabs-rof'each-mix .were press cured, and=thetnsile strength and the relative resistance to abrasion ofjthe vulcanizates wasmeasuredrthe results being. shown in Table II. The two mixes-had-zthe' following es r o A Y B Ordinary broken-down smoked sheet 100 Treated rubber 100.

Carbon black 50 3 50 Pine tar 5 Palm oil 1 Zinc oxi 1 7 i 2' 2 Zincsoaps of cocoanut-oilacids Q3 3 Methylated polyethylene polyamines (accelerator); 1. 1 1. 0 Acetone'diphenylamine condensate (antioxidant). 1.25 T ,1.

TABLE 11:; i "1 Plasticity w i Z I A B Broken-down rubber (belore"compounding) 5 60. 0.

; compounded rnix nn; I 49.5- 60.5 V

, Tensile strength (Zbs./sq. in.)

Cure 'A B 7 I y it t v H 515 min. at 45lbs 3840 3981 min. .at 45 lbs 3780 3907 min. at 45 lbs 3570 3675 '90 min. at 45 lbs 3590' 1 3600 I Z Relative abrasion resistance Cure A B 45min.at45lbs "86; 11 1- 25 60m1n.at45lbs '100. 1l2" 75 min. at 45 lbs... 7 116 140 min. at 451195-.- a 119 i151 Average relative valu 2% indispensable ,s'ofteners from mixB, made. p'osf sistance to abrasion;

p y d ied rubbers, etc; 1:

obvious modifications i will suggest Sthemselves;

sible 'by thisinvention, results ina superior V1171:

canized product} particularly in respect. to its rewithout departing a from the principle ol thein-v vention, and itis not desired to limit the invention otherwise than as set "forth-in the appended Having thus describedinvention, what 1 claim and desire toprote ct bymetters Patent 1 s-:' l. A process of breaking downfcrude rubber prior to the addition of compounding "and/ 0rv canizing ingredients which; comprises adding to the crude rubber a compound'selected from the roup consisting of lea'dtdioxide and lead'se squi V I oxide, in an amount sufficient to reduce the 1s cosity of the rubber and mjlling the rubberifor a r 1 time and at a temperature suriicient to; produce a decrease in. viscosity"? 1 2: A- process or breaking 'Jdown crude rubber; prior to theladdition of compounding and/ or Pann in re e s w m-c m e a din ilpi the crude rubber" a Q QmDQ I Q selected mm the group consisting or lead'dioxi'deland leaQdTSQSCfi I V oxide, in an 'amount suflicient' to reduce the cosity of the rubber and milling the rubber "for;

a time and; at a temperaturesnillcient =to proj-j' duceadecre ase in viscosityiand'to decomposethe added reagent so that substantially no trace of it remains. v, I, s 1L3 Agplasticized and broken downcruderubber product substantially identical with" the product produced as set forth in claimg said product hav-' ing substantially no tendency i d go h x Q-l \tIQp c'h r n -C n- It, will be seen that the omissionof the 3 

